Graphs and Scales

Graphs and Scales

Basic

Scales are used to indicate values on graphs. Values are normally shown on the heavier graph lines. The distance between successive values must be regular.

Check the scale to see by what value the scale is increasing: it may go up in 1s, 2s, 5s, 10s or some other increment. Use the lighter lines to determine intermediate values.

The example below shows a scale which increases in single values. The red line shows a value of 6. The purple line is between 7 and 8, and it is seven faint lines after the value of 7 which gives it a value of 7 + 0.7 = 7.7.

scale showing 6 and 7.7

The next example shows the scale going up in increments of 5. The red line indicates a value of 25. The purple line is 6 faint lines past the value of 35. Each of the 2 faint lines is worth 1, so 6 lines is worth 3. The value of the purple line is therefore 35 + 3 = 38.

scale showing 25 and 38

Examples

1. What is wrong with this scale?

badly set out scale

Answer: The scale is not consistent.

The scale increases with a value of 1 until it reaches 8, then it increases with a value of 2. The scale is not consistent.

2. What is the value of the purple line?

length of purple line on scale

Answer: 29

The scale increases in 5s, each set of 2 lines is worth 1. It is 2 lines short of 30, therefore 29.